Modern computers typically include a power control system which receives signals indicating if the computer is to be powered on or powered off. For example, the power button on a computer may not be directly connected to the computer's power supply. Instead, pressing the power button generates a signal, often called a power management event (PME), which is received by power control circuitry within the computer that is always active as long as the computer is connected to power. This circuitry, in turn, activates the power supply of the computer, if the computer was off, thus turning the computer on. Likewise, if the computer was already on, the PME event would cause the computer to shutdown.
In addition, certain components of the computer may be configured to always remain available to some extent, regardless of the power state of the overall computer. For example, a network interface controller (NIC) may be configured to remain on regardless of the power state of the computer. When the NIC receives a certain packet, often referred to as a magic packet, the NIC may generate a power on signal, similar to the one described above. Thus, a computer that is in an off state may be woken up through a local area network (LAN) connection. Remote power on of a computer over a network is often referred to as Wake on LAN (WOL) and the magic packet may also be referred to as a WOL packet.